Studies are described in this research proposal to fully characterize a newly isolated acidic Ca2 ion binding brain protein which is very similar to muscle troponin C. Detailed analyses of this protein purified from bovine, porcine, and rabbit brain will include: 1) Molecular weight determination by ultracentrifugation; 2) Complete amino acid sequence determination by automated and manual techniques; 3) Immunoligical characterization by radioimmunoassay, complement fixation and immunodiffusion; 4) Studies of the nature of the divalent cation binding sites by ultrafiltration binding studies and by chemical modification. Comparative comparison between; 5) Direct brain TN-C from all three sources and authentic muscle TN-C by polyacrylamide gel electrophoresis under denaturing and non-denaturing conditions, comparative tryptic peptide fingerprint analysis and immunological techniques. The biological characterization of brain TN-C using immunological techniques will include determination of 1) Distribution in central and peripheral nerves in rabbits 2) Organ specificity 3) Cell type specificity and 4) Appearance during development. Studies concerning the possible role of brain TN-C and other components of the muscle contraction system in a contractile mechanism for CA-2 ion mediated neurotransmitter release are also described in detail. It is hoped these studies will provide insight into the molecular mechanism of CA2 ion mediated secretory processes.